The most effectual method of accomplishing this object is by stratagem. Demonstrations are made at several points at the same time: bodies of troops are thrown across, after nightfall, in rowboats or by flying-bridges, to get possession of the opposite bank. The vanguard of light cavalry may cross by swimming. The pontoniers should have their bridge equipage in readiness near the intended point of passage, so that it can be thrown across with the greatest possible rapidity, while the advanced guards are still able to keep the enemy at a distance. Under favorable circumstances the pontoniers will have the bridge in readiness for the passage of the army before the enemy can collect his troops upon the threatened point. Cannon-balls and hollow shot are the most effectual means for destroying an enemy's bridge when our batteries can be planted within reach. When this cannot be done, we must resort to fire-boats, floating rafts, &c., to accomplish our object. Operations of this kind carried on in the night, are most likely to succeed. To protect bridges from the action of these floating bodies, stockades, or floating chevaux-de-frise are constructed across the stream at some distance above the bridge; strong cables, or chains stretched directly across the river, or with an angle up stream, may be used in place of stockades, or in conjunction with them. Guards should be stationed above the bridge, with boats, ropes, grapnels, &c., for the purpose of arresting all floating bodies and drawing thorn ashore, or directing them safely through the _draw_ in the bridge arrangement. The troops especially charged with the construction and management of the various kinds of military bridges, are denominated _pontoniers_. The duties of these troops are arduous and important, and, in a country like ours, intersected by numerous water-courses, the success of a campaign will often depend upon their skill and efficiency. _Sapping_.--This is a general term applied to the operations of forming trenches, along which troops may approach a work without being exposed to the fire of the besieged. In addition to the ordinary sapping-tools, such as shovels, picks, gabion-forks, &c., used in constructing trenches, there will also be required a considerable amount of sapping materials, such as gabions, fascines, sap-fagots, sandbags, &c. The _gabion_ is a cylindrical basket of twigs, about two feet in diameter, and some three feet in length, and without a bottom. It is made by driving into the ground, in a circular form, a number of small pickets about an inch in diameter, and of the length required for the gabion. Twigs are wattled between the pickets like ordinary basket-work, and fastened at the ends by withs or packthread. Gabions are used in forming saps, batteries, blindages, powder-magazines, and in revetting the steep slopes of field-works.